 It is analogous to the innate immune system found in animals, and commonly precedes a slower systemic (whole plant) response, which ultimately leads to systemic acquired resistance (SAR).HR can be observed in the vast majority of plant species and is induced by a wide range of plant pathogens such as oomycetes, viruses, fungi and even insects.HR is commonly thought of as an effective defence strategy against biotrophic plant pathogens, which require living tissue to gain nutrients.